The present disclosure relates to optical data storage media. More particularly the present disclosure relates to holographic storage media as well as methods of making and using the same.
The rapid growth of information technology industry has led to an increasing demand for data storage systems. Optical data storage, wherein reading or writing of data is accomplished by shining light on, for example a disc, provides advantages over data recorded in media which must be read by other means, for example a magnetically sensitive head for reading magnetic media, or a needle for reading media recorded in vinyl. And, more data can be stored in smaller media optically than can be stored in vinyl media. Further, since contact is not required to read the data, optical media are not as vulnerable to deterioration over periods of repeated use as vinyl media.
Nonetheless, conventional optical data storage media does have limitations as known to one skilled in the art. Alternative data storage methods include holographic storage. This is an optical data storage method in which the data is represented as holograms. Early attempts at holographic storage relied on a page-based approach, i.e., where the bits of digital information are encoded into volume holograms as two-dimensional arrays of logical zeros and ones that traversed a ‘slice’ of the necessarily linear media onto which the holograms were recorded. More recent research into holographic data storage has focused on a bit-wise approach, where each bit (or few bits) of information is represented by a hologram localized to a microscopic volume within a medium to create a region that reflects the readout light. Materials capable of accommodating a bit-wise data storage approach are highly sought after as the equipment utilized to read and write to such material is either currently commercially available, or readily provided with modifications to readily commercially available reading and writing equipment. Further, holographic data storage by the bit-wise approach is more robust to temperature, wavelength, intensity variations, and vibration than holographic data stored using the page-based approach. In order to be optimally useful in the recordation of holograms, and in particular, micro-holograms, bit-wise data storage materials must be non-linear and further exhibit desirable refractive index change in response to recording light. The magnitude of the refractive index modulations produced in the material by the recording light defines the diffraction efficiency for a given system configuration, which translates to the signal to noise ratio, bit error rate, and the achievable data density.
Thus, there remains a need for optical data storage media that can exhibit a nonlinear (or “threshold”) response to the recording light intensity and that is suitable for bit-wise holographic data storage. In particular, it would be advantageous for holograms stored in the media to be limited in depth so that increased capacity could be realized. It would be further desirable for such data storage media to be written in such a way that refractive index of the surrounding media is not significantly altered and that a substantial degradation of hologram efficiency at various depths is not seen. Desirably, any such materials provided would have sufficient refractive index change to support diffraction efficiencies so as to be capable of recording high-density micro-holographic data, thereby further expanding the storage capacity of the material.